It is known in the art to extend the inherent photosensitive response of silver halide emulsions by the incorporation therein of spectral sensitizing dyes. In color photographic elements a plurality of silver halide emulsions are employed, sensitized to different portions of the spectrum, e.g. a red-sensitized silver halide emulsion, a green-sensitized silver halide emulsion and a blue-sensitized silver halide emulsion. In panchromatically sensitized emulsions, generally a combination of dyes are employed to provide the requisite sensitivity from about 400 nm to 650 nm.
Diffusion transfer photographic products and processes are known to the art and details relating thereto can be found in U.S. Pat. Nos. 2,983,606; 3,415,644; 3,415,645; 3,415,646; 3,473,925; 3,482,972; 3,551,406; 3,573,042; 3,573,043; 3,573,044; 3,576,625; 3,576,626; 3,578,540; 3,569,333; 3,579,333; 3,594,164; 3,594,165; 3,597,200, 3,647,437; 3,672,486; 3,672,890; 3,705,184; 3,752,836; 3,857,865, all of which are incorporated here in their entirety. Essentially, diffusion transfer photographic products and processes involve film units having a photosensitive system including at least one silver halide layer, usually integrated with an image-providing material. For example, a photosensitive element comprising a support carrying a red-sensitive silver halide emulsion having associated therewith a cyan dye developer, a green-sensitive silver halide emulsion having associated therewith a magenta dye developer and a blue-sensitive silver halide emulsion having associated therewith a yellow dye developer is known. After photoexposure, the photosensitive system is developed to establish an imagewise distribution of a diffusible image-providing material, at least a portion of which is transferred by diffusion to an image-receiving layer capable of mordanting or otherwise fixing the transferred image-providing material. In some diffusion transfer products, the transfer image is viewed by reflection after separation of the image-receiving element from the photosensitive system. In other products, however, such separation is not required and instead the transfer image-receiving layer is viewed against the reflecting background usually provided by a dispersion of a white reflecting pigment, such as, for example, titanium dioxide. The latter type of film unit is generally referred to in the art as integral negative-positive film units and is described, for example, in the above mentioned U.S. Pat. Nos. 3,415,644 and 3,594,165.
U.S. Pat. No. 3,362,819 teaches image-receiving elements particularly adapted for employment in the preceding diffusion transfer processes which comprise a support layer possessing on one surface thereof, in sequence, a polymeric acid layer, preferably an inert timing or spacer layer, and an image-receiving layer adapted to provide a visible image upon transfer to said layer of diffusible dye image-forming substance.
Commercial color photographic elements generally employ more than one green sensitizing dye for the green-sensitive emulsion. The use of a plurality of green dyes is necessitated by the failure of a single dye to provide a sufficiently broad spectral response without extending into the red region.
Other problems associated with sensitizing dyes include the inability to adsorb sufficiently to the silver halide grain to avoid displacement, and lack of shelf life stability.
It is the object of this invention to provide an improved spectral sensitizing dye for the green region, and photosensitive elements and photographic film units containing such a sensitizing dye. This and other objects of the invention will become apparent from the following detailed description of the invention.